1. Field of the Invention
The present invention relates to an interference detecting circuit and method thereof, and more particularly, to an interference detecting circuit utilizing synchronization symbols and method thereof suitable for a digital TV system.
2. Description of the Prior Art
Please refer to FIG. 1, which is a diagram showing the specification of a prior art digital TV signal format used in the U.S.A. The digital TV signal used in the U.S.A. complies with the specifications defined by an Advanced Television Systems Committee (ATSC). As defined in the ATSC specification, each field comprises 313 segments and the starting segment of each field is a Field SYNC, which has a known and fixed pattern.
When the ATSC digital TV system and the NTSC analog TV system are broadcasting TV programs simultaneously, it may happen that an ATSC digital TV signal and an NTSC analog TV signal on the same frequency band interfere with each other. Therefore, the ATSC system needs to detect whether the received ATSC digital TV signal has interfered with the NTSC analog TV signal or not. If yes, then the ATSC system has to filter it out; otherwise, the ATSC system omits the filtering process to prevent the final picture quality from being deteriorated by additional interference induced by undesired filtering.
The prior art interference detecting method applied to a digital TV receiver is for comparing the pattern of the received Field SYNC with a known Field SYNC. According to the comparison result, the interference detecting method estimates the seriousness of the interference, and selectively performs interference rejection filtering on the received digital TV signal.
Due to digital TV signals being affected by interference resulting from noise or transmission path variation, the received Field SYNC in the digital TV signal may be distorted. The result is that the digital TV receiver is unable to identify the Field SYNC transmitted by the received digital TV signal, or erroneously activates the interference rejection filtering because of the distortion of the received Field SYNC. Therefore, the prior art interference detection malfunctions.